4f9d1b15b4
This fixes two race conditions in LoopControl::Attach(). The first is that after LOOP_CTL_GET_FREE, the path is not be available until it has been processed by ueventd. This can be fixed by adding a timeout parameter and a call to WaitForFile(). Second, it is possible (albeit unlikely), given that loop devices are now being used more aggressively, that two processes race when attempting LOOP_SET_FD. In this case, one process will win, and the other will fail with EBUSY. We can handle this case by retrying the operation while respecting the same timeout parameter. Bug: 135771280 Test: libdm_test gtest Change-Id: Icf9facc3ca28fdb6ff5c78612d3dc183fa47b1f3
56 lines
1.8 KiB
C++
56 lines
1.8 KiB
C++
// Copyright (C) 2019 The Android Open Source Project
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include "utility.h"
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#include <errno.h>
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#include <unistd.h>
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#include <thread>
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using namespace std::literals;
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namespace android {
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namespace dm {
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bool WaitForCondition(const std::function<WaitResult()>& condition,
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const std::chrono::milliseconds& timeout_ms) {
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auto start_time = std::chrono::steady_clock::now();
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while (true) {
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auto result = condition();
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if (result == WaitResult::Done) return true;
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if (result == WaitResult::Fail) return false;
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std::this_thread::sleep_for(20ms);
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auto now = std::chrono::steady_clock::now();
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auto time_elapsed = std::chrono::duration_cast<std::chrono::milliseconds>(now - start_time);
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if (time_elapsed > timeout_ms) return false;
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}
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}
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bool WaitForFile(const std::string& path, const std::chrono::milliseconds& timeout_ms) {
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auto condition = [&]() -> WaitResult {
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// If the file exists but returns EPERM or something, we consider the
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// condition met.
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if (access(path.c_str(), F_OK) != 0) {
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if (errno == ENOENT) return WaitResult::Wait;
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}
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return WaitResult::Done;
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};
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return WaitForCondition(condition, timeout_ms);
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}
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} // namespace dm
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} // namespace android
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